This application is not related to any pending United States or international patent application.
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When a well is drilled from the earth""s surface into an oil bearing formation, the oil may be forced to the earth""s surface by formation pressure. However, when the formation pressure is insufficient to force the oil to the earth""s surface, either due to an inherent low pressure formation or, when a formation has been produced for an extended period of time such that the formation pressure has diminished, it is then necessary to pump the oil from the formation to the earth""s surface. Pumping of oil wells has historically been accomplished primarily through the use of sucker rod pumps in which a string of sucker rods is reciprocated within tubing extending from the earth""s surface into the oil producing formation. At the bottom of the string of sucker rods is a reciprocated pump. To actuate the pump the sucker rods are vertically reciprocated. The constantly repeated reversal of stresses in reciprocated pumping operations results in fairly high wear rates and frequent failures.
To overcome problems inherent with reciprocated sucker rod pumps, down-hole fluid operated pumps have been developed. These pumps typically include a fluid operated pump motor that actuates a pumping mechanism. The most common type of down-hole fluid operated deep well pumps employ pump engines that reciprocate a pump piston. In some instances, the hydraulic fluid used to produce pump action is mixed with the production fluid to flow commingled back to the earth""s surface. In some installations, a separate return line is employed so that the hydraulic fluid employed for pumping action is recirculated back to the earth""s surface independently of the production fluid. While the latter type system works effectively, it requires parallel hydraulic operating fluid lines in addition to the production fluid passageway and thus the installation of this latter type of pump is more difficult. The most commonly employed hydraulically actuated down-hole pumps utilize the arrangement wherein power fluid is forced down a central tubing to actuate a reciprocating pump engine to force production fluid into an annular area between a casing and the power tubing to flow to the earth""s surface and in which the spent power fluid is commingled with the production fluid. This system requires only concentric piping that is substantially easier to install than parallel piping.
A typical hydraulically actuated down-hole pump has a fluid powered motor that produces reciprocal action and a reciprocating pump with the motor piston and the pump piston in axial alignment and connected by a piston rod. A typical pump is in the order of 1.9xe2x80x3 to 3.8xe2x80x3 inches in diameter and from 6.5xe2x80x2 to 25xe2x80x2 feet or longer and is positioned in a bottom hole assembly of a well casing. The well casing is typically in the order of about 4xc2xdxe2x80x3 to 9xe2x80x3 inches in diameter and the tubing used to supply high pressure hydraulic fluid to actuate the pump may typically be from 1xc2xdxe2x80x3 to 2xc2xdxe2x80x3 inches in diameter. The produced fluid flows back to the earth""s surface in the annular area between the interior of the casing and the exterior of the tubing.
A basic description of the operation and function of a bottom hole pump can be obtained from U.S. Pat. No. 2,081,227 entitled, xe2x80x9cFLUID OPERATED DEEP WELL PUMPxe2x80x9d that issued on May 25, 1937. This patent indicates that hydraulically actuated down-hole pumping has been used for at least sixty years and is an indication of the success of hydraulic down-hole pumping.
Hydraulically actuated pumps must be removed periodically from a well for repair of worn parts and replacement of seals. The life of a hydraulically actuated pump depends upon many factors, a primary one being the nature of the fluid being handledxe2x80x94that is, whether the fluid is inherently corrosive or includes entrained abrasive components such as sand.
In order to obtain more pumping power, especially for operation at greater depthsxe2x80x94multi-engine pumps have been employed. For an example of a multi-engine pump reference may be had to U.S. Pat. No. 3,653,786 entitled, xe2x80x9cFLUID OPERATED PUMP ASSEMBLY WITH TANDEM ENGINESxe2x80x9d issued Apr. 4, 1972. In a pump of this design, two fluid powered motors are positioned in tandem, one above the other, with the motor pistons connected by an axially in-line piston rod. Some dual engine configurations require porting to the exterior of the pump to provide fluid paths around various components. This can result in larger diameter well casing requirements thereby increasing the expense of the installation. In addition, some multi-engine pumps require additional annual seals on the exterior of the pump for externally ported flow paths. These additional seals increase the cost of construction and impose additional maintenance expense.
For additional background information relating to hydraulically actuated down-hole pumps employing more than one pump piston, reference may be had to U.S. Pat. No. 5,209,651 entitled, xe2x80x9cMULTIPLE ENGINE DEEP WELL PUMPxe2x80x9d that issued on May 11, 1993; U.S. Pat. No. 5,651,664 entitled, xe2x80x9cxe2x80x9dFREExe2x80x9d COIL TUBING DOWNHOLE JET PUMP APPARATUS AND METHODxe2x80x9d that issued on Jul. 29, 1997; and U.S. Pat. No. 5,667,364 entitled, xe2x80x9cDOWNHOLE HYDRAULIC PUMP APPARATUS HAVING A xe2x80x9cFREExe2x80x9d JET PUMP AND SAFETY VALVE ASSEMBLY AND METHODxe2x80x9d that issued on Sep. 16, 1997.
The present invention is a down-hole reciprocating hydraulic piston pump for use in oil wells. The pump of this invention is suitable for high volume deep well applications and is particularly adaptable for use in remote areas such as jungles, deserts, cold climates and so forth where space is limited and transportation is not readily available.
The pump to be described herein can be utilized in two basic systems. That is, in the first type of pumping system the pump can be employed as a fixed type pump meaning that it is physically attached to the lower end of a string of tubing suspended from the earth""s surface, the tubing running in casing and having a packer at the lower end that receives the down-hole pump. In this type of fixed installation the tubing must be removed in order to replace or repair the down-hole pump. The second type of pumping system that can employ the pump of this invention is referred to as the free-pump system in which the pump is not installed at the lower end of a string of tubing but is introduced directly into tubing at the earth""s surface, the pump moving down within the tubing to seat itself at the lower end of the tubing. By reversing the direction of fluid flow to force fluid in the well annulus up through the tubing, the pump can be hydraulically moved from its operating position back to the earth""s surface.
When the pump of this invention is used in a fixed installation, no external seals are required. When used as a free style, only one seal, typically an O-ring, is required at the top of the pump and a metal-to-metal seal at the bottom of the pump. This compares with other designs, designs that use as many as six or more external seals.
The pump of this invention is a reciprocating hydraulic piston pump, double acting and balanced with two or more engine pistons and one or more production pistons. Power fluid is introduced to the down-hole pump through power tubing and is directed by the hydraulic valving in the engine to actuate the engine pistons.
Up stroke motion of the power pistons is produced by power fluid directed by valving through an annular area between an engine outer tube and an engine cylinder to the bottom of the engine pistons. The pistons are connected by rods, the lower engine connecting rod being hollow. As the pistons move up, spent power fluid is discharged from the upper side of the engine pistons through a hollow engine middle rod and ports to the top side of the engine pistons and discharge ports on an engine valve body to an exit where the fluid exits the piston into the annular area exterior of the well tubing. At the same time production fluid is taken in through production intake valving on the power side of the production pistons and discharged from the top side of the production pistons through discharge valving and to the production exit. The produced fluid and the spent power fluid are commingled and flow back to the earth""s surface in the well annular area within the casing and exterior of the power tubing.
On the down stroke, power fluid is introduced through ports and an engine valve to the top of the upper engine piston and through an upper hollow engine rod to the top of the lower engine piston. Spent fluid as a result of the downward movement of the engine pistons is discharged from the lower side of the engine pistons into an annular area between the engine outer tubes and the outside of the engine cylinder through discharge ports. At the same time, the production piston or pistons, which are connected to the engine pistons by a metal rod, begin to move downward. Production is taken on in the top of the production pistons through intake production valves and through the annular area between the pump and an outer tube and the outside of the pump end cylinder and through a ported lower plug. Production fluid is discharged from the bottom of the production piston through the discharge production valve assembly.
The length of the pump stroke is controlled by a ported rod which is located on the top of the upper engine piston. Grooves in a valve rod direct power fluid to the engine valve which directs power fluid to the top or bottom of the engine pistons according to the position of the pistons to cause the pistons to vertically reciprocate.
A better understanding of the invention will be obtained from the following description and claims, taken in conjunction with the attached drawings.